Modular vehicle window assemblies have enjoyed wide-spread use. Conventional modular vehicle window assemblies include a sheet-like panel of glass having a polymeric gasket or casing disposed about the peripheral edge. The polymeric gasket may encapsulate the edge of the panel as well as a predetermined portion of each side of the panel. Such a "three-sided" encapsulation not only spaces the panel from the vehicle opening, but also seals the outer surface of the panel against the vehicle. More recently, single-sided assemblies have been designed in which a polymeric gasket or spacer is located on only one side of the window panel, preferably near the peripheral edge. Such single-sided gaskets enable mounting of the resultant window assembly in the vehicle such that the outer glass surface is flush with the vehicle body exterior thereby reducing wind drag and noise and increasing fuel economy and aesthetic appeal. Both the three-sided and single-sided gaskets are made from thermoplastic compounds such as polyvinyl chloride, polyolefins, thermoplastic urethanes, thermoplastic elastomers, as well as thermosetting compounds such as reaction-injection molded (RIM) urethane, EPDM, rubbers, etc.
Urethane sealants are used commonly by the automobile manufacturers to securely attach the above-described window assemblies to the vehicle body. The adhesive is typically located on the inside surface of the glass window panel adjacent the gasket and pressed into contact with the sheet metal forming the window opening. This metal-to-glass bond has proven successful in surviving moisture and humidity exposure as well as providing a strong bond. Disadvantages associated with the metal-to-glass bond include requiring a wider black-out coating or area, typically formed with a layer of opaque ceramic frit fired onto the inside glass surface, to conceal the bond, and a larger pinch-weld flange on the vehicle to receive the bond.
Another bonding technique used to mount the window assemblies in the vehicle opening is an adhesive between an adhesion-promoting compound on the gasket material and the metal flange forming the opening. To date, the strength of such alternative bond has not been equivalent to or as satisfactory as the bond strength and environmental stability of adhesive bonds achieved directly between the metal flange to the glass panel. When a failure of such an alternative bond occurs, the failure usually occurs along the interface of the adhesion-promoting primer and the gasket, which can result in water leaks and wind noise. A further disadvantage with this particular technique is that once the adhesion-promoting compound is applied, the urethane sealant must be applied within a relatively short time to obtain the best available bond. The adhesion-promoting compound has a very short idle time once applied. This requires that the compound and urethane sealant be applied to the panel by the window installer at the time of installation.
Yet, an advantage provided by this alternative bonding technique is that the window panel may have a narrower black-out or frit boundary and the window opening may be defined by a narrower pinch-weld flange thereby reducing vehicle weight while increasing the field of view through the window. However, because the window panels are becoming an important structural component of the vehicle, failure of the bond between the panel and the vehicle may result in further damage to the vehicle or compromise vehicle safety.
Obtaining sufficient window-to-vehicle bond strength has in the past often required a series of complex, involved, or time-consuming preparation steps at the vehicle manufacturing site. For example, application or reapplication of an adhesion-promoting primer compound to the gasket or vehicle flange immediately prior to window assembly installation is often required to achieve necessary bonding strength. Such steps have added cost to the vehicle while increasing manufacturing time, among other disadvantages.
Accordingly, a need was recognized for an improved bond between a gasketed window assembly and a vehicle which would provide an improved bond strength while achieving increased window opening area, reduced vehicle weight, increased fuel economy, and long-term weather resilience, particularly exposure to moisture. Further, a reduction in time-consuming window installation steps at the vehicle manufacturing site was also desired.